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Square Foot Rooftop Gardening

Square foot gardeningis a method of gardening that was described and popularized by Mel Bartholomew. The basic concept is simple: measure out your garden beds into equal squares (4 feet by 4 feet) and then plant individual crops into each square following specific spacing recommendations for each crop. The square foot method is intended to eliminate the inefficiencies of standard row planting, making vegetable crops easier to plant, maintain, and harvest. Bartholomew’s book about square foot gardening was first published in 1981. From that book came a television series on PBS, various other books and updated versions of the original book, a square foot gardening product line, and the Square Foot Gardening Foundation.

As a long time gardener, I had been familiar with Bartholomew’s book and its basic premise for a while but had never read it until recently. I found the book to be basically what I expected: a description of how to garden in squares instead of rows. I can see how this system could be very simple, attractive, and efficient while simultaneously producing decent sized yields; however I felt like Bartholomew’s description of the process made gardening into a very methodical, calculated, and meticulous task bordering on joyless. I’m sure that’s not how he sees it (nor how it really is), but then again, he’s a retired engineer [insert smiley face here].

For a long time I’ve had an interest in green roofs. I even went to graduate school to study them. So when I got to the part in Bartholomew’s book where he talks about square foot gardening on rooftops, I was intrigued. Green roofs (along with rooftop vegetable gardening) have become fairly common in urban areas in the past decade or two. And for good reason. Green roofs offer myriad benefits including mitigating storm water runoff (and the numerous sub-benefits involved with that), reducing the urban heat island effect, increasing a building’s energy efficiency, and re-introducing green space and wildlife habitat that was lost when a building was built.

Vegetable gardening on rooftops is a practical solution for residents of urban areas where space for gardens on the ground is limited. Restaurants – like NobleRotin Portland, Oregon and CaféOsagein St. Louis, Missouri – have found that they can grow some of the produce and herbs they need on their rooftops while simultaneously setting themselves apart from other restaurants. There are also a few urban farming operations on rooftops (BrooklynGrangeand EagleStreetRooftopFarmfor example). Michigan State University (an institution with one of the most prominent green roof research labs in the U.S.) has a researchprogramdedicated to improving rooftop vegetable crop production. So with this recent trend of growing food on rooftops, I was curious to read what Bartholomew was saying about the subject more than thirty years ago, back when green roof vegetable gardening was less than mainstream.

The reality is that square foot rooftop gardening gets only a brief mention in Bartholomew’s book (at least in the first edition – perhaps he has more to say about it in more recent editions), but what he does have to say is relevant.

Rooftops are windy:

“Stay away from plants that grow tall, have delicate stems, or that might be blown over when they are mature and filled with ripening fruit…The wind can be unmerciful to a plant; it whips the leaves about and can dry out the plant in short order.”

Rooftops are hot:

“The other big consideration for rooftop growing is heat buildup…These conditions will naturally affect both the frequency and amount of watering the garden will need.”

Rooftopshave weight limits:

“The soil in your rooftop garden should be as light and porous (yet still be water retentive) as possible. Mix in lots of vermiculite and peat moss.”

Each of these three considerations (wind, heat, and weight) continue to be considerations for any vegetated roof whether it includes vegetable crops or not. Yet people are figuring out how to overcome these obstacles, constructing and maintaining incredible rooftop gardens that are both productive and beneficial.

In future posts, I intend to elaborate more on this topic, profiling individuals, groups, and organizations that are making this sort of thing happen. Comment below and share something about your favorite rooftop garden and/or recommend a rooftop garden that should be profiled in an upcoming post.